Musical instrument



March 27, 1934.. N. A. PALMGREN MUSICAL INSTRUMENT Filed June 29, 1933INVENTOR NILsARV/D PALMGRE/V 'L ATTORNEY Patented Mar. 27, 1934 MUSICALINSTRUMENT Nils Arvid Palmgren, Gottenborg, Sweden Application June 29,1933, Serial No. 678,134 111 Sweden July 28, 1932 4 Claims.

This invention relates to musical instruments associated with anelectric sound reproduction system, and having a series of mechanicalvibratory members tuned to acoustic frequencies and comprisingelectrically conductive material, an electrode disposed near suchvibratory members and electrically insulated from them and formingtherewith electrical condensers, the distance between electrode andvibratory member being difierent for different vibratory members.

In musical instruments having a number of vibratory members, such asstrings or the like and electrically conductive plates or electrodesarranged adjacent thereto and forming together with the vibratorymembers, condensers serving to transform the vibrations of the stringsto electrical impulses, it is of great importance that'disturbingelectrostatic fields are prevented from acting between the string andthe electrode. Such electrostatic fields may reach an intensitycomparable to that of the variations in strength of the field caused bythe vibrations of the strings.

The object of the present invention is to eliminate the disturbances byelectrostatically screening the electrodes, i. e. by enclosing them in arelatively tight system of bodies of constant potential.

The invention is illustrated in the accompanying drawing which:

Figure 1 is a diagram showing the electrical arrangement of one form ofthe invention.

Fig. 2 is a plan view of the frame, the system of strings and theelectrodes of a form of the invention, and

Fig. 3 is a section along the line 33 of Fig. 2.

In Fig. 1 the numeral 1 denotes a string near which is located anelectrode 2. The electrode is screened on one side by the string'and onthe other side by a member 3 electrically connected to the string. Thestring 1 is connected to the positive poleof a source of electricalcurrent 4, the negative pole of which is connected to the electrode 2through the resistance 5. The electrostatic fields between the electrodeand the string 1 and between the electrode and the screen 3 cannot bedisturbed by extraneous fields. The

connection 6 between the electrode 2 and the grid of the amplifier tubeis also screened.

In the form of the, invention illustrated in Figs. 2 and 3 a series ofstrings 9 are shown strung on a cast iron frame 8. The frame istherefore 60 in electrical contact with the strings. At a short distancefrom the strings are located two electrodes 10 and 11. As shown in Fig.3 the electrode 10 comprises a layer 12 of metallic substance applied toa thicker plate 13 of electrically insulating material. The frame 8 isextended to form a plate 14 which covers the whole electrode and towhich the electrode is adjustably fixed by means of adjusting screws 15and 16. The electrostatc screen is here formed by the series of strings9, the frame 8 and the plate 14 in conjunction. By fixing the electrodeto the part 14 of the frame which screens the electrode the advantage isobtained that the distance between the string and the electrode can beaccurately adjusted and maintained independent of changes in temperatureand humidity.

I claim 3. A musical instrument according to claim 1 in which thevibratory members comprise strings strung on a metallic frame,characterized in that the electrostatic screen on one side of theelectrode is formed by the series of strings and on the other side by apart of the frame.

4. A musical instrument having a metallic frame, a series of vibratorystrings strung thereon, a series of electrodes located adjacent thestrings, the series of strings forming an electrostatic screen on oneside of the electrodes and a part ofthe frame forming a screen on theother side thereof, and adjusting screws for fixing the electrodes tothat part of the frame which serves 100 to screen them.

NILS ARVID PALMGREN.

